Method of pressure sensing with a pressure sensor having a sensor membrane and a compensation membrane

Abstract

The invention provides for a method of sensing pressure with a pressure sensor having a sensor membrane and a compensation membrane. The pressure sensor also includes a power supply, a controller; and a charge amplifier, a charge injector and two switches arranged in signal communication with the controller. The method includes the step of connecting the charge amplifier to the switches via a sensor capacitor C s in parallel with a reference capacitor C r in parallel with a parasitic capacitance C p to ground, the charge injector and charge amplifier arranged in parallel connection between the capacitors and the controller. The method also includes the step of operating the switches, via the controller, to determine a charge imbalance indicative of a pressure difference between the sensor and compensation membranes.

1. A method of sensing pressure with a pressure sensor having a sensor membrane and a compensation membrane, the pressure sensor also having a power supply, a controller; and a charge amplifier, a charge injector and two switches arranged in signal communication with the controller, the method comprising:
 connecting the charge amplifier to the switches via a sensor capacitor C s  in parallel with a reference capacitor C r  in parallel with a parasitic capacitance C p  to ground, the charge injector and charge amplifier arranged in parallel connection between the capacitors and the controller; and 
 operating the switches, via the controller, to determine a charge imbalance indicative of a pressure difference between the sensor and compensation membranes. 
 
   
   
     2. The method of  claim 1 , wherein the step of connecting includes connecting the power supply to supply constant reference voltages V 1  and V 2  to the respective switches. 
   
   
     3. The method of  claim 2 , wherein voltages V 1  and V 2  are alternately switched onto capacitors C r  or C s  to charge said capacitors with respective voltages V r  and V s . 
   
   
     4. The method of  claim 3 , wherein the voltages V 1  or V 2  applied to respective capacitors C r  or C s  are fed through the capacitors C r  or C s  to charge amplifier as voltage V in , the charge amplifier amplifying the voltage V in  to a voltage V out . 
   
   
     5. The method of  claim 4 , wherein voltage V in  provides a measure of charge imbalance in the sensor when capacitor C r  is switched to voltage V 2 , capacitor C s  is switched to voltage V 1 , the charge amplifier is reset to force voltage V in  to a fixed voltage V r  and the charge injector is set to known charge state Q I1 , the total stored charge in the capacitors Q 1  determined by Q 1 =C r (V 2 −V r )+C s (V 1 −V r )+Q I1 . 
   
   
     6. The method of  claim 5 , wherein capacitor C r  is connected to voltage V 1 , capacitor C s  is connected to voltage V 2 , and an output from the charge amplifier is monitored by the controller with feedback applied to the charge injector such that the total charge is balanced by the charge injector injecting a charge of Q I1 −Q I2  to force voltage V in  equal to voltage V r , so that the total stored charge in the capacitors Q 2  is given by Q 2 =C r (V 1 −V r )+C s (V 2 −V r )+Q I2 . 
   
   
     7. The method of  claim 6 , wherein the controller applies feedback to the sensor to force Q 1 =Q 2 , with a digital output from the controller configured to output a charge difference result of Q I1 −Q I2 =(V 1 −V 2 )·(C r −C s ).